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Collision of 2 black holes

Collision of 2 black holes


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There is a large number of visible Supernovas. Each week - about a 20 Supernovas Type 1a around the Universe.

Is there collisions of Black Holes? What is this collision called?

E.g. 2 black holes come close to each other. There are event horizons for both black holes, will this made such collision super long in Earth's time?


It's called a black hole merger, or coalescence. Here a simulation video.

Even the formation of the event horizons of the two initial black holes takes "super long" in Earth's time. That's similar with the merger. On the other hand we are very close to the completed merger within a short "Earth's" time seen from a distance, as soon as the merger starts. General relativity as well as quantum theory are incomplete with what will happen very close to a presumed singularity or at the presumed event horizon; this will remain disputed until a satisfying theory of quantum gravity is found.

Mergers of black holes are likely to occur, e.g. when two galaxies collide, the momentum of the central supermassive black holes (SMBH) is slowed down by consumption of gas, dust and stars, until the SMBHs merge to the central SMBH of the merged galaxy. Here a galaxy merger simulation.

Here a simulation of the coalescence of two black holes within a collapsing star.

More on black hole binaries on Wikipedia.


Black hole collision may have exploded with light

When two black holes spiral around each other and ultimately collide, they send out ripples in space and time called gravitational waves. Because black holes do not give off light, these events are not expected to shine with any light waves, or electromagnetic radiation. Graduate Center, CUNY astrophysicists K. E. Saavik Ford and Barry McKernan have posited ways in which a black hole merger might explode with light. Now, for the first time, astronomers have seen evidence of one of these light-producing scenarios. Their findings are available in the current issues of Physical Review Letters.

A team consisting of scientists from The Graduate Center, CUNY Caltech's Zwicky Transient Facility (ZTF) Borough of Manhattan Community College (BMCC) and The American Museum of Natural History (AMNH) spotted what appears to be a flare of light from a pair of coalescing black holes. The event (called S190521g) was first identified by the National Science Foundation's (NSF) Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo detector on May 21, 2019. As the black holes merged, jiggling space and time, they sent out gravitational waves. Shortly thereafter, scientists at ZTF -- which is located at the Palomar Observatory near San Diego -- reviewed their recordings of the same the event and spotted what may be a flare of light coming from the coalescing black holes.

"At the center of most galaxies lurks a supermassive black hole. It's surrounded by a swarm of stars and dead stars, including black holes," said study coauthor Ford, a professor with the Graduate Center, BMCC and AMNH. "These objects swarm like angry bees around the monstrous queen bee at the center. They can briefly find gravitational partners and pair up but usually lose their partners quickly to the mad dance. But in a supermassive black hole's disk, the flowing gas converts the mosh pit of the swarm to a classical minuet, organizing the black holes so they can pair up," she says.

Once the black holes merge, the new, now-larger black hole experiences a kick that sends it off in a random direction, and it plows through the gas in the disk. "It is the reaction of the gas to this speeding bullet that creates a bright flare, visible with telescopes," said co-author McKernan, an astrophysics professor with The Graduate Center, BMCC and AMNH.

"This supermassive black hole was burbling along for years before this more abrupt flare," said the study's lead author Matthew Graham, a research professor of astronomy at Caltech and the project scientist for ZTF. "The flare occurred on the right timescale, and in the right location, to be coincident with the gravitational-wave event. In our study, we conclude that the flare is likely the result of a black hole merger, but we cannot completely rule out other possibilities."

"ZTF was specifically designed to identify new, rare, and variable types of astronomical activity like this," said NSF Division of Astronomical Science Director Ralph Gaume. "NSF support of new technology continues to expand how we can track such events."

Such a flare is predicted to begin days to weeks after the initial splash of gravitational waves produced during the merger. In this case, ZTF did not catch the event right away, but when the scientists went back and looked through archival ZTF images months later, they found a signal that started days after the May 2019 gravitational-wave event. ZTF observed the flare slowly fade over the period of a month.

The scientists attempted to get a more detailed look at the light of the supermassive black hole, called a spectrum, but by the time they looked, the flare had already faded. A spectrum would have offered more support for the idea that the flare came from merging black holes within the disk of the supermassive black hole. However, the researchers say they were able to largely rule out other possible causes for the observed flare, including a supernova or a tidal disruption event, which occurs when a black hole essentially eats a star.

What is more, the team says it is not likely that the flare came from the usual rumblings of the supermassive black hole, which regularly feeds off its surrounding disk. Using the Catalina Real-Time Transient Survey, led by Caltech, they were able to assess the behavior of the black hole over the past 15 years, and found that its activity was relatively normal until May of 2019, when it suddenly intensified.

"Supermassive black holes like this one have flares all the time. They are not quiet objects, but the timing, size, and location of this flare was spectacular," said co-author Mansi Kasliwal (MS '07, PhD '11), an assistant professor of astronomy at Caltech. "The reason looking for flares like this is so important is that it helps enormously with astrophysics and cosmology questions. If we can do this again and detect light from the mergers of other black holes, then we can nail down the homes of these black holes and learn more about their origins."

The newly formed black hole should cause another flare in the next few years. The process of merging gave the object a kick that should cause it to enter the supermassive black hole's disk again, producing another flash of light that ZTF should be able to see.


Astronomers watch on as two black hole behemoths get ready for a collision

A galaxy roughly 2.5 billion light years away has a pair of supermassive black holes (inset image). The locations of the black holes are lit up by warm gas and bright stars that surround the objects. Image credit: A.D. Goulding et al./Astrophysical Journal Letters 2019

Astronomers have spotted a distant pair of titanic black holes headed for a collision. Each black hole’s mass is more than 800 million times that of our Sun. As the two gradually draw closer together in a death spiral, they will begin sending gravitational waves rippling through space-time. Those cosmic ripples will join the as-yet-undetected background noise of gravitational waves from other supermassive black holes.

Even before the destined collision, the gravitational waves emanating from the supermassive black hole pair will dwarf those previously detected from the mergers of much smaller black holes and neutron stars.

“Supermassive black hole binaries produce the loudest gravitational waves in the Universe,” says co-discoverer Chiara Mingarelli, an associate research scientist at the Flatiron Institute’s Center for Computational Astrophysics in New York City, United States. Gravitational waves from supermassive black hole pairs “are a million times louder than those detected by LIGO.”

The study was led by Andy Goulding, an associate research scholar at Princeton University, New Jersey, United States. Goulding, Mingarelli and collaborators from Princeton and the U.S. Naval Research Laboratory in Washington, D.C., United States, reported the discovery on 10 July 2019 in The Astrophysical Journal Letters .

The two supermassive black holes are especially interesting because they are around 2.5 billion light-years away from Earth. Since looking at distant objects in astronomy is like looking back in time, the pair belong to a Universe 2.5 billion years younger than our own. Coincidentally, that’s roughly the same amount of time the astronomers estimate the black holes will take to begin producing powerful gravitational waves.

In the present-day Universe, the black holes are already emitting these gravitational waves, but even at light speed the waves won’t reach us for billions of years. The duo is still useful, though. Their discovery can help scientists estimate how many nearby supermassive black holes are emitting gravitational waves that we could detect right now.

Detecting the gravitational wave background will help resolve some of the biggest unknowns in astronomy, such as how often galaxies merge and whether supermassive black hole pairs merge at all or become stuck in a near-endless waltz around each other.

“It’s a major embarrassment for astronomy that we don’t know if supermassive black holes merge,” says study co-author Jenny Greene, a professor of astrophysical sciences at Princeton. “For everyone in black hole physics, observationally this is a long-standing puzzle that we need to solve.”

Supermassive black holes contain millions or even billions of Suns’ worth of mass. Nearly all galaxies, including the Milky Way, contain at least one of the behemoths at their core. When galaxies merge, their supermassive black holes meet up and begin orbiting one another. Over time, this orbit tightens as gas and stars pass between the black holes and steal energy.

Pardo and Mingarelli predict that in an optimistic scenario there are about 112 nearby supermassive black holes emitting gravitational waves. Image credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

Once the supermassive black holes get close enough, though, this energy theft all but stops. Some theoretical studies suggest that black holes then stall at around one parsec (roughly 3.2 light years) apart. This slowdown lasts nearly indefinitely and is known as the ‘final parsec problem’. In this scenario, only very rare groups of three or more supermassive black holes result in mergers.

Astronomers can’t just look for stalled pairs because long before the black holes are one parsec apart, they’re too close to distinguish as two separate objects. Moreover, they don’t produce strong gravitational waves until they overcome the final-parsec hurdle and get closer together. (Observed as they were 2.5 billion years ago, the newfound supermassive black holes appear about 430 parsecs apart.)

If the final parsec problem doesn’t exist, then astronomers expect that the Universe is filled with the clamour of gravitational waves from supermassive black hole pairs. “This noise is called the gravitational wave background, and it’s a bit like a chaotic chorus of crickets chirping in the night,” says Goulding. “You can’t discern one cricket from another, but the volume of the noise helps you estimate how many crickets are out there.” (When two supermassive black holes finally collide and combine, they send out a thundering chirp that dwarfs all others. Such an event is brief and extraordinarily rare, though, so scientists don’t expect to detect one any time soon.)

The gravitational waves generated by supermassive black hole pairs are outside the frequencies currently observable by experiments such as LIGO and Virgo. Instead, gravitational wave hunters rely on arrays of special stars called pulsars that act like metronomes. The rapidly spinning stars send out radio waves in a steady rhythm. If a passing gravitational wave stretches or compresses the space between Earth and the pulsar, the rhythm is slightly thrown off.

Detecting the gravitational wave background using one of these pulsar timing arrays takes patience and plenty of monitored stars. A single pulsar’s rhythm might be disrupted by only a few hundred nanoseconds over a decade. The louder the background noise, the bigger the timing disruption and the sooner the first detection will be made.

Goulding, Greene and the other observational astronomers on the team detected the two titans with the Hubble Space Telescope. Although supermassive black holes aren’t directly visible through an optical telescope, they are surrounded by bright clumps of luminous stars and warm gas drawn in by the powerful gravitational tug. For its time in history, the galaxy harbouring the newfound supermassive black hole pair “is basically the most luminous galaxy in the Universe,” Goulding says. What’s more, the galaxy’s core is shooting out two unusually colossal plumes of gas. After the researchers pointed the Hubble Space Telescope at the galaxy to uncover the origins of its spectacular gas clouds, they discovered that the system contained not one but two massive black holes.

The observationalists then teamed up with gravitational wave physicists Mingarelli and Princeton graduate student Kris Pardo to interpret the findings in the context of the gravitational wave background. The discovery provides an anchor point for estimating how many supermassive black hole pairs are within detection distance of Earth. Previous estimates relied on computer models of how often galaxies merge, rather than actual observations of supermassive black hole pairs.

Based on the findings, Pardo and Mingarelli predict that in an optimistic scenario there are about 112 nearby supermassive black holes emitting gravitational waves. The first detection of the gravitational wave background from supermassive black holes should therefore come within the next five years or so. If such a detection isn’t made, that would be evidence that the final parsec problem may be insurmountable. The team is currently looking at other galaxies similar to the one harbouring the newfound supermassive black hole pair. Finding additional pairs will help them further hone their predictions.

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Black hole collision may have exploded with light

Artist's concept of a supermassive black hole and its surrounding disk of gas. Embedded within this disk are two smaller black holes orbiting one another. Using data from the Zwicky Transient Facility (ZTF) at Palomar Observatory, researchers have identified a flare of light suspected to have come from one such binary pair soon after they merged into a larger black hole. The merger of the black holes would have caused them to move in one direction within the disk, plowing through the gas in such a way to create a light flare. The finding, while not confirmed, could amount to the first time that light has been seen from a coalescing pair of black holes. These merging black holes were first spotted on May 21, 2019, by the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo detector, which picked up gravitational waves generated by the merger. Credit: Caltech/R. Hurt (IPAC)

When two black holes spiral around each other and ultimately collide, they send out ripples in space and time called gravitational waves. Because black holes do not give off light, these events are not expected to shine with any light waves, or electromagnetic radiation. Graduate Center, CUNY astrophysicists K. E. Saavik Ford and Barry McKernan have posited ways in which a black hole merger might explode with light. Now, for the first time, astronomers have seen evidence of one of these light-producing scenarios. Their findings are available in the current issues of Physical Review Letters.

A team consisting of scientists from The Graduate Center, CUNY Caltech's Zwicky Transient Facility (ZTF) Borough of Manhattan Community College (BMCC) and The American Museum of Natural History (AMNH) spotted what appears to be a flare of light from a pair of coalescing black holes. The event (called S190521g) was first identified by the National Science Foundation's (NSF) Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo detector on May 21, 2019. As the black holes merged, jiggling space and time, they sent out gravitational waves. Shortly thereafter, scientists at ZTF—which is located at the Palomar Observatory near San Diego—reviewed their recordings of the same the event and spotted what may be a flare of light coming from the coalescing black holes.

"At the center of most galaxies lurks a supermassive black hole. It's surrounded by a swarm of stars and dead stars, including black holes," said study coauthor Ford, a professor with the Graduate Center, BMCC and AMNH. "These objects swarm like angry bees around the monstrous queen bee at the center. They can briefly find gravitational partners and pair up but usually lose their partners quickly to the mad dance. But in a supermassive black hole's disk, the flowing gas converts the mosh pit of the swarm to a classical minuet, organizing the black holes so they can pair up," she says.

Once the black holes merge, the new, now-larger black hole experiences a kick that sends it off in a random direction, and it plows through the gas in the disk. "It is the reaction of the gas to this speeding bullet that creates a bright flare, visible with telescopes," said co-author McKernan, an astrophysics professor with The Graduate Center, BMCC and AMNH.

"This supermassive black hole was burbling along for years before this more abrupt flare," said the study's lead author Matthew Graham, a research professor of astronomy at Caltech and the project scientist for ZTF. "The flare occurred on the right timescale, and in the right location, to be coincident with the gravitational-wave event. In our study, we conclude that the flare is likely the result of a black hole merger, but we cannot completely rule out other possibilities."

"ZTF was specifically designed to identify new, rare, and variable types of astronomical activity like this," said NSF Division of Astronomical Science Director Ralph Gaume. "NSF support of new technology continues to expand how we can track such events."

Such a flare is predicted to begin days to weeks after the initial splash of gravitational waves produced during the merger. In this case, ZTF did not catch the event right away, but when the scientists went back and looked through archival ZTF images months later, they found a signal that started days after the May 2019 gravitational-wave event. ZTF observed the flare slowly fade over the period of a month.

The scientists attempted to get a more detailed look at the light of the supermassive black hole, called a spectrum, but by the time they looked, the flare had already faded. A spectrum would have offered more support for the idea that the flare came from merging black holes within the disk of the supermassive black hole. However, the researchers say they were able to largely rule out other possible causes for the observed flare, including a supernova or a tidal disruption event, which occurs when a black hole essentially eats a star.

What is more, the team says it is not likely that the flare came from the usual rumblings of the supermassive black hole, which regularly feeds off its surrounding disk. Using the Catalina Real-Time Transient Survey, led by Caltech, they were able to assess the behavior of the black hole over the past 15 years, and found that its activity was relatively normal until May of 2019, when it suddenly intensified.

"Supermassive black holes like this one have flares all the time. They are not quiet objects, but the timing, size, and location of this flare was spectacular," said co-author Mansi Kasliwal (MS '07, Ph.D. '11), an assistant professor of astronomy at Caltech. "The reason looking for flares like this is so important is that it helps enormously with astrophysics and cosmology questions. If we can do this again and detect light from the mergers of other black holes, then we can nail down the homes of these black holes and learn more about their origins."

The newly formed black hole should cause another flare in the next few years. The process of merging gave the object a kick that should cause it to enter the supermassive black hole's disk again, producing another flash of light that ZTF should be able to see.

The paper is titled, "A Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational Wave Event GW190521g."


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Collision of two black holes. / Anninos, Peter Hobill, David Seidel, Edward Smarr, Larry Suen, Wai Mo.

In: Physical review letters , Vol. 71, No. 18, 1993, p. 2851-2854.

Research output : Contribution to journal › Article › peer-review

T1 - Collision of two black holes

N1 - Copyright: Copyright 2015 Elsevier B.V., All rights reserved.

N2 - We study the head-on collision of two equal-mass, nonrotating black holes. We consider various cases, from holes surrounded by a common horizon to holes separated by about 20M, where M is the mass of each hole. The wave forms and energy output are computed, showing that normal modes of the final black hole are clearly excited. We also estimate analytically the total gravitational radiation emitted, considering tidal heating of horizons and other effects. The analytic calculations, perturbation theory, and strong-field, nonlinear numerical calculations agree very well with each other.

AB - We study the head-on collision of two equal-mass, nonrotating black holes. We consider various cases, from holes surrounded by a common horizon to holes separated by about 20M, where M is the mass of each hole. The wave forms and energy output are computed, showing that normal modes of the final black hole are clearly excited. We also estimate analytically the total gravitational radiation emitted, considering tidal heating of horizons and other effects. The analytic calculations, perturbation theory, and strong-field, nonlinear numerical calculations agree very well with each other.


Shaking Up the Universe

Gravitational waves are so weak that it took a hundred years for physicists and engineers to come up with instruments, such as LIGO and Virgo, that can detect them. Yet, they are so powerful that they can shake up the universe for billions of light-years in all directions.

The black hole collision detected in 2017 originated with two black holes in orbit of one another. One black hole weighed about 25 times more than the sun the other about 31 times more. They continued to orbit each other until they collided in an event that took place about 1.8 billion light-years away, resulting in a spinning black hole with a mass of about 53 times the sun, according to the NSF.

That mass was converted into gravitational-wave energy — enough to jiggle our most sensitive instruments here on Earth, 1.8 billion light-years away.

The LIGO and Virgo teams predict that, as they fine-tune their instruments, they will be able to detect gravitational wave signals weekly. And as with every new window into the universe, our wildest imagination will be nothing to the surprises we are sure to discover.

Interested in all things in outer space and exploration? We are too. Take a look at open positions at Northrop Grumman and consider joining our team.

Popular


Black hole collision may have exploded with light

This artist's concept shows a supermassive black hole and its surrounding disk of gas. Embedded within this disk are two smaller black holes orbiting one another. Using data from the Zwicky Transient Facility (ZTF) at Palomar Observatory, an international team of researchers have identified a flare of light suspected to have come from one such binary pair soon after they merged into a larger black hole. The finding could be the first time that light has been seen from a coalescing pair of black holes. Credit: Caltech/R. Hurt (IPAC)

An international team of astronomers, including researchers from the University of Minnesota, have seen what might amount to the first light ever detected from a black hole merger.

When two black holes spiral around each other and ultimately collide, they send out ripples in space and time called gravitational waves. Because black holes do not give off light, these events are not expected to shine with any light waves, or electromagnetic radiation. But some theorists have come up with ways in which a black hole merger might explode with light.

Now, for the first time, astronomers have seen evidence for one of these light-producing scenarios. The research is published in the journal Physical Review Letters, the American Physical Society’s flagship publication.

With the help of Caltech's Zwicky Transient Facility (ZTF), funded by the National Science Foundation (NSF) and located at Palomar Observatory near San Diego, the scientists have spotted what might be a flare of light from a pair of coalescing black holes. The black hole merger was first spotted by the NSF's Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo detector on May 21, 2019, in an event called S190521g. As the black holes merged, jiggling space and time, they sent out gravitational waves.

While this was happening, ZTF was performing its robotic survey of the sky that captured all kinds of objects that flare, erupt, or otherwise vary in the night sky. One flare the survey caught, generated by a distant active supermassive black hole, or quasar, called J1249+3449, was pinpointed to the region of the gravitational-wave event S190521g.

“One of the big questions in astrophysics is where black hole mergers generally come from,” said University of Minnesota physics and astronomy Assistant Professor Michael Coughlin, who is part of the ZTF team and a co-author of the publication. “‘Small’ black holes in the vicinity of ‘big’ black holes are one possibility, and the potential detection of an optical counterpart to a binary black hole merger in the vicinity of one of these supermassive black holes gives us a clue that this might be an important place these are produced.”

Coughlin, who helps lead the searches for gravitational-wave counterparts for binary neutron star and neutron star black holes with ZTF, said this detection also gives as a hint that while these binary black holes themselves do not emit light, they might disrupt their surroundings enough to make it possible to see their aftermath.

“This supermassive black hole was burbling along for years before this more abrupt flare,” said Matthew Graham, a research professor of astronomy at Caltech and lead author of the study. “The flare occurred on the right timescale, and in the right location, to be coincident with the gravitational-wave event. In our study, we conclude that the flare is likely the result of a black hole merger, but we cannot completely rule out other possibilities.”

How do two merging black holes erupt with light? In the scenario outlined by Graham and his colleagues, two partner black holes were nestled within a disk surrounding a much larger black hole.

“At the center of most galaxies lurks a supermassive black hole. It's surrounded by a swarm of stars and dead stars, including black holes,” said co-author K. E. Saavik Ford of the City University of New York (CUNY) Graduate Center, the Borough of Manhattan Community College (BMCC), and the American Museum of Natural History (AMNH). “These objects swarm like angry bees around the monstrous queen bee at the center. They can briefly find gravitational partners and pair up but usually lose their partners quickly to the mad dance. But in a supermassive black hole's disk, the flowing gas converts the mosh pit of the swarm to a classical minuet, organizing the black holes so they can pair up,” she said.

Once the black holes merge, the new, now-larger black hole experiences a kick that sends it off in a random direction, and it plows through the gas in the disk.

“It is the reaction of the gas to this speeding bullet that creates a bright flare, visible with telescopes,” said co-author Barry McKernan, also of the CUNY Graduate Center, BMCC, and AMNH.

Such a flare is predicted to begin days to weeks after the initial splash of gravitational waves produced during the merger. In this case, ZTF did not catch the event right away, but when the scientists went back and looked through archival ZTF images months later, they found a signal that started days after the May 2019 gravitational-wave event. ZTF observed the flare slowly fade over the period of a month.

The scientists attempted to get a more detailed look at the light of the supermassive black hole, called a spectrum, but by the time they looked, the flare had already faded. A spectrum would have offered more support for the idea that the flare came from merging black holes within the disk of the supermassive black hole. However, the researchers say they were able to largely rule out other possible causes for the observed flare, including a supernova or a tidal disruption event, which occurs when a black hole essentially eats a star.

What is more, the team says it is not likely that the flare came from the usual rumblings of the supermassive black hole, which regularly feeds off its surrounding disk. Using the Catalina Real-Time Transient Survey, led by Caltech, they were able to assess the behavior of the black hole over the past 15 years, and found that its activity was relatively normal until May of 2019, when it suddenly intensified.

“Supermassive black holes like this one have flares all the time. They are not quiet objects, but the timing, size, and location of this flare was spectacular,” said co-author Mansi Kasliwal, an assistant professor of astronomy at Caltech. “The reason looking for flares like this is so important is that it helps enormously with astrophysics and cosmology questions. If we can do this again and detect light from the mergers of other black holes, then we can nail down the homes of these black holes and learn more about their origins.”

The newly formed black hole should cause another flare in the next few years. The process of merging gave the object a kick that should cause it to enter the supermassive black hole's disk again, producing another flash of light that ZTF should be able to see.

The research was funded by the NSF, NASA, the Heising-Simons Foundation, and the GROWTH (Global Relay of Observatories Watching Transients Happen) program. ZTF is also funded by an international collaboration of partners, with additional support from NASA, the Heising-Simons Foundation, members of the Space Innovation Council at Caltech, and Caltech itself.

To read the full research paper entitled “Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational Wave Event GW190521g,” visit the Physical Review Letters website.


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2020 September 8
GW190521: Unexpected Black Holes Collide
Illustration Credit: Raúl Rubio (Virgo Valencia Group, The Virgo Collaboration)

Explanation: How do black holes like this form? The two black holes that spiraled together to produce the gravitational wave event GW190521 were not only the most massive black holes ever seen by LIGO and VIRGO so far, their masses -- 66 and 85 solar masses -- were unprecedented and unexpected. Lower mass black holes, below about 65 solar masses are known to form in supernova explosions. Conversely, higher mass black holes, above about 135 solar masses, are thought to be created by very massive stars imploding after they use up their weight-bearing nuclear-fusion-producing elements. How such intermediate mass black holes came to exist is yet unknown, although one hypothesis holds that they result from consecutive collisions of stars and black holes in dense star clusters. Featured is an illustration of the black holes just before collision, annotated with arrows indicating their spin axes. In the illustration, the spiral waves indicate the production of gravitational radiation, while the surrounding stars highlight the possibility that the merger occurred in a star cluster. Seen last year but emanating from an epoch when the universe was only about half its present age (z

0.8), black hole merger GW190521 is the farthest yet detected, to within measurement errors.


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 October 20
When Black Holes Collide
Video Credit & Copyright: Simulating Extreme Spacetimes Collaboration

Explanation: What happens when two black holes collide? This extreme scenario likely occurs in the centers of some merging galaxies and multiple star systems. The featured video shows a computer animation of the final stages of such a merger, while highlighting the gravitational lensing effects that would appear on a background starfield. The black regions indicate the event horizons of the dynamic duo, while a surrounding ring of shifting background stars indicates the position of their combined Einstein ring. All background stars not only have images visible outside of this Einstein ring, but also have one or more companion images visible on the inside. Eventually the two black holes coalesce. The end stages of such a merger may provide a strong and predictable blast of gravitational radiation, a much sought after form of radiation different than light that has never yet been directly observed.


Black hole collision?

In all the videos I've seen, they do orbit, just the time between stable orbit and merger is extremely short, so they do effectively fall into one another.

Probably not stars are tiny things and galaxies are huge - the probability that any two stars collide is negligible, and even though a black hole presents a much larger cross-section to hit (partly due to gravity pulling in nearby stars), it's still pretty tiny.

Now, it's likely that a huge amount of gas will come crashing down into the central black holes, causing them to flare up brightly, and it's possible that a handful of stars may be redirected such that they're torn apart by a black hole.

And mergers of SMBHs are very, very slow - their orbits are often large, and, while they can drop down to around a parsec from one another just by throwing stars outwards, it's unclear how they manage to get any closer (if they do).

As the black holes get closer and closer together, they exponentially speed up while doing so. For stellar mass black holes, the time from the first moment they're close enough to produce gravitational waves to the moment they're completely merged is usually only a second. To an observer this would probably look like them suddenly crashing into one another.

Probably not a very large amount. Lots of space is completely empty and even the most massive black holes aren't very big. Probably a few dozen stars at most, if any at all, as a rough guess.

2nd: will the black holes in andromeda or Milky Way swallow a large amount of stars as they spiral each other before merging?

No, not especially. Now they will take a long time to properly merge - the two black holes. And they may never do so. Those right next to them might be in for a bumpy ride, but nearly every estimate that I've read says there's a high possibility that no stars themselves would collide with anything as the spaces between them are just that big.

If black holes have infinite gravity

Black holes don't have infinite gravity - certainly not outside the event horizon.

they should swallow at least half of the galaxy while in the process of merging

Why? If they have 'infinite' gravity, they should swallow the universe. But they don't, so they don't.

A black hole with a mass of a million stars has the gravity of a million stars, no more. Since there's 200-400 billion stars in this galaxy alone, you can do the maths in your head there to within an order of magnitude.

You could completely remove the super massive black holes in both the MW and A and neither galaxy would "notice", on the whole.

Yes, they do tend to have strong gravitational attraction but that’s inescapable for only matter that enters the event horizon. Also, the gravitational ‘reach’ or to what extent a black hole’s gravity interferes with its surrounding matter depends on how massive it is (there might be some other factor that I’m unaware of though), So to answer your question, how much matter they’d take in simply depends on how much matter is around them and will be influenced by their gravity, and its likely not half the galaxy :)

The only time the gravity could be argued to be infinite is in the singularity, and both are taken as indications that General Relativity is wrong. 46AU from Sagittarius A* for example (just past the orbit of Neptune), its gravity is no stronger than what we experience here on Earth, and a parsec away, it's just fifty billionths of that. Now, compared to the gravity of the Sun, that's absolutely huge. But nowhere near enough to consume half the galaxy. And the central bulge of the galaxy weighs around 20 billion solar masses, so while an object 10kpc out would be pulled in by a force of 2.8×10 -11m/s2, the black hole itself only contributes one six thousandth of that. Basically, unless you're right near a black hole, it's a pretty minor player (excluding if it becomes a quasar, in which case it can heat up an entire galaxy, halting star formation).


Watch the video: Η σύγκρουση με τον γαλαξία της Ανδρομέδας. Astronio X #2 (June 2022).


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